Compositions of polytetramethylene ether glycols and polyoxy alkylene polyether polyols having a low degree of unsaturation

ABSTRACT

Thus, there is provided according to the present invention polyol compositions comprising 
     (A) a polytetramethylene ether glycol, and 
     (B) a difunctional active hydrogen compound-initiated polyoxyalkylene polyether polyol having a degree of unsaturation of not greater than 0.04 milliequivalents per gram of said polyether polyol.

This is a divisional of application Ser. No. 08/678,028 filed Jul. 10,1996, now pending.

FIELD OF THE INVENTION

This invention relates to blends of poly-tetramethylene polyetherglycols and polyoxyalkylene polyether polyols having a low degree ofunsaturation of 0.04 or less, and to the cast elastomers, spandexfibers, and thermoplastic polyurethanes made therefrom.

BACKGROUND OF THE INVENTION

Polyurethane elastomers often utilize one or more polytetramethyleneether glycols (PTMEG's) as a polyol component to react with one or morepolyisocyanates such as MDI because they can impart to the elastomer thehigh level of mechanical properties required for specific applications.PTMEG's are often used for such applications where high tensilestrength, low compression set, high resilience, and/or a high modulus ofelasticity are required. PTMEG's, however, can be difficult andexpensive to make due to the availability of starting materials and theformation of undesired side-reaction products during synthesis.

It would therefore be desirable to provide polyol compositions that canbe used to manufacture high-quality polyurethane elastomers whilereducing the amount of PTMEG required.

SUMMARY OF THE INVENTION

Thus, there is provided according to the present invention polyolcompositions comprising

(A) a polytetramethylene ether glycol, and

(B) a difunctional active hydrogen compound-initiated polyoxyalkylenepolyether polyol having a degree of unsaturation of not greater than0.04 milliequivalents per gram of said polyether polyol.

The polyol compositions according to the present invention can be usedfor the manufacture of polyurethane elastomers via a one-shot techniqueor a prepolymer technique. Elastomers based on the polyol compositionsof the invention exhibit a good combination of properties such astensile strength, compression set, resilience, and/or a modulus ofelasticity, which often previously required the use pure PTMEG. Otherproperties, such as elongation and resilience, can often be improved byutilizing the blend compositions of the invention.

Thus, in one embodiment of the invention, there is provided a prepolymerobtained by reacting a polyol composition comprising at least theabove-described PTMEG and a polyoxyalkylene polyether polyol having adegree of unsaturation of 0.04 or less, with an organic polyisocyanate.The prepolymer may be isocyanate terminated by adding asub-stoichiometric amount of the polyol composition to the isocyanate,or hydroxyl terminated by adding to the isocyanate a molar excess of thepolyol composition.

In another embodiment of the invention, there is provided an elastomermade by reacting an organic di- or polyisocyanate with the polyolcomposition, optionally in the presence of a hydroxyl and/or aminefunctional chain extender at an equivalent NCO:OH ratio of at least1.5:1, where the polyol composition is made up of at least PTMEG and apolyoxyalkylene polyether polyol having a degree of unsaturation of 0.04or less. The polyol composition of the invention may be a principalpolyol component of the urethane elastomer-forming reaction mixture(i.e., one-shot method) or it may first be incorporated into aprepolymer prior to incorporation into the urethane elastomer-formingreaction (i.e., prepolymer methods).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

PTMEG's useful in the practice of the invention generally have a numberaverage molecular weight ranging from 500 to 5000, preferably 800 to3000, more preferably from 1000 to 2600. Techniques for the manufactureof PTMEG are well-known in the art, such as described in U.S. Pat. Nos.4,294,997 and 4,213,000, the disclosures of which are incorporatedherein by reference. Examples of useful PTMEG's include POLYTHF® 650,POLYTHF® 1000, POLYTHF® 2000, and POLYTHF® 2900.

PTMEG's are generally synthesized by a ring-opening chain extensionreaction of the monomeric tetrahydrofuran (THF). In one well-knownmethod, the ring-opening reaction is catalyzed by fluorosulfonic acid,followed by hydrolysis of sulfate ester groups and water extraction ofthe acid, followed by neutralization and drying. In many cases, thePTMEG will be solid at room temperature because of its high degree ofcrystallinity. In the event one desires to employ a room temperatureliquid PTMEG, the THF can be copolymerized with alkylene oxides (alsoknown as cyclic ethers or monoepoxides) as suggested in U.S. Pat. No.4,211,854, incorporated herein by reference. Such copolymers have anA-B-A block-heteric structure, wherein the A blocks are randomcopolymers of tetrahydrofuran and alkylene oxides, and the B block ismade up of polytetramethylene oxides.

The cyclic ethers copolymerizable with tetrahydrofuran are notparticularly limited, provided that they are cyclic ethers capable ofring-opening polymerization, and may include, for example, 3-memberedcyclic ethers, 4-membered cyclic ethers, cyclic ethers such astetrahydrofuran derivatives, and cyclic ethers such as 1,3-dioxolan,trioxane, etc. Examples of cyclic ethers include ethylene oxide1,2-butene oxide, 1,2-hexene oxide, 1,2-tert-butyl ethylene oxide,cyclohexene oxide, 1,2-octene oxide, cyclohexylethylene oxide, styreneoxide, phenyl glycidyl ether, allyl glycidyl ether, 1,2-decene oxide,1,2-octadecene oxide, epichlorohydrin, epibromohydrin, epiiodohydrin,perfluoropropylene oxide, cyclopentene oxide, 1,2-pentene oxide,propylene oxide, isobutylene oxide, trimethyleneethylene oxide,tetramethyleneethylene oxide, styrene oxide, 1,1-diphenylethylene oxide,epifluorohydrin, epichlorohydrin, epibromohydrin, epiiodohydrin,1,1,1-trifluoro-2-propylene oxide, 1,1,1-trifluoro-2-methyl-2-propyleneoxide, 1,1,1-trichloro-2-methyl-3-bromo-2-propylene oxide,1,1,1-tribromo-2-butyleneoxide, 1,1,1-trifluoro-2-butyleneoxide,1,1,1-trichloro-2-butylene oxide, oxetane, 3-methyloxetane,3,,3-dimethyloxetane, 3,3-diethyloxetane, 3,3-bis(chloromethyl)oxetane,3,3-bis(bromomethyl)oxetane, 3,3-bis(iodomethyl)oxetane,3,3-bis(fluoromethyl)oxetane, 2-methyltetrahydrofuran,3-methyltetrahydrofuran, 2-methyl-3-chloromethyltetrahydrofuran,3-ethyltetrahydrofuran, 3-isopropyltetrahydrofuran,2-isobutyltetrahydrofuran, 7-oxabicyclo(2,2,1)heptane, and the like.

The content of the copolymerized cyclic ether, if present, in a PTMEGmay be within the range of from 5 to 95% by weight, but when obtaining acopolymerized polyetherglycol containing oxytetramethylene groups as amain component which is effective as the soft segment in a polyurethaneelastomer such as spandex, the amount of the cyclic ether in the A blockcopolymerizable with THF is generally from 30 to 70 weight %. In theevent one chooses to randomly copolymerize cyclic ethers with THF acrossthe whole copolymer, the amount of cyclic ether may range from 5 to 60weight % of the copolymer.

Additionally, in the synthesizing reaction of PTMEG, a part of thestarting THF may be replaced with an oligomer of PTMEG as the startingmaterial. Further, in the synthesizing reaction of a copolymerizedpolyetherglycol, an oligomer of PTMEG or an oligomer of thepolyetherglycol to be synthesized may also be added as a part of thestarting material to carry out the reaction. In such a case, theoligomer generally has a molecular weight lower than the polymer to besynthesized. More specifically, one may use an oligomer having anumber-average molecular weight within the range of from 100 to 800 whensynthesizing a polymer with a number-average molecular weight of 1000 ormore, and an oligomer with a number-average molecular weight of 100 to2000 when synthesizing a polymer with a number-average molecular weightof 3000 or more. Also, an oligomer separated by fractional extraction orvacuum distillation from the PTMEG or the copolymerized polyetherglycolsynthesized may be employed. Such an oligomer may be added in an amountof up to 10% by weight into the starting monomer.

The degree of polymerization tends to decrease as the reactiontemperature is increased and therefore, and also in view of thepolymerization yield, the polymerization temperature should preferablybe -10° to 120° C., more preferably 30° to 80° C. If the temperatureexceeds 120° C., the yield decreases. The time required for the reactionis generally 0.5 to 20 hours, although it may vary depending upon thecatalyst amount and the reaction temperature. The reaction may becarried out in any system generally employed such as tank type or towertype vessel. It is also feasible by either batch or continuous system.

Catalysts used in the preparation of PTMEG are well known, and includeany cationic catalyst, such as strongly acidic cationic exchange resins,fuming sulfuric acids, and boron trifluorides.

The polyol blends of the present invention comprise a difunctionalactive hydrogen compound-initiated polyoxyalkylene polyether polyol.Difunctional active hydrogen compound-initiated polyoxyalkylenepolyether polyols useful in the practice of the invention should havenumber average molecular weights suitable for the particularapplication, and generally from 400 to 7000, preferably from 1000 to6500, more preferably from 1500 to 3500, and most preferably from 2000to 3000.

The hydroxyl numbers of the polyoxyalkylene polyether polyols used inthe invention correspond to the desired number average molecular weightby the formula:

    OH=(f) 56,100/equivalent weight

For most applications, suitable hydroxyl numbers for the polyoxyalkylenepolyether polyol ranges from 15 to 250, and most often from 25 to 120.

The polyoxyalkylene polyether polyols used in the invention have adegree of unsaturation of 0.04 milliequivalents KOH/g of polyol or less,preferably 0.03 or less, more preferably 0.02 or less.

The structure of the polyoxyalkylene polyether polyol contains a nucleusof a difunctional active hydrogen compound initiator compound containingat least two hydrogen atoms reactive to alkylene oxides. Specifically,the reactive hydrogen atoms on the initiator compound should besufficiently labile to open up the epoxide ring of ethylene oxide. Theinitiator compound has a relatively low molecular weight, generallyunder 400, more preferably under 150.

Examples of initiator compounds useful in the practice of this inventioninclude, but are not limited to, ethylene glycol, propylene glycol,diethylene glycol, dipropylene glycol, 2,3-butylene glycol, 1,3-butyleneglycol, 1,5-pentanediol, 1,6-hexanediol, and the like. Another class ofreactive hydrogen compounds that can be used are the alkyl amines andalkylene polyamines having two reactive hydrogen atoms, such asmethylamine, ethylamine, propylamine, butylamine, hexylamine,ethylenediamine, diethylenediamine, 1,6-hexanediamine, and the like. Itmay be necessary to select catalysts or adjust reaction conditions thatwould allow both primary and secondary amine hydrogens to ring-open thealkylene oxides in order to render the monoamines difunctional.Conversely, it may be necessary to select catalysts or adjust reactionconditions to favor only primary amine hydrogens in order to render thediamines difunctional. Cyclic amines such as piperazine,2-methylpiperazine, and 2,5-dimethylpiperazine can also be used. Amidesconstitute a further class of such reactive hydrogen compounds, such asacetamide, succinamide, and benzene sulfonamide. A still further classof such reactive hydrogen compounds are the dicarboxylic acids, such asadipic acid and the like. The initiator can also be one containingdifferent functional groups having reactive hydrogen atoms, also, suchas glycolic acid, ethanolamine, and the like.

In one preferred embodiment, the polyoxyalkylene polyether polyols usedin the invention contain at least one hydrophobic block made frompropylene oxide or a mixture of propylene oxide and other cyclic ethers.Such other cyclic ethers are either of the type that are hydrophobicrelative to polyoxyethylene groups; or if of a hydrophilic character,are admixed with propylene oxide only in those relative amounts thatwill not render the polyol ineffective for its ultimate application. Thehydrophobic block may consist of a homoblock of oxypropylene groups or ablock of randomly distributed oxypropylene groups and other oxyalkylenegroups. As an alternative to or in combination with propylene oxide,butylene oxide may also be used, as it also exhibits hydrophobicproperties and yields polyols having a low degree of unsaturation.

The polyether of the invention may also be prepared by the additionreaction between a suitable initiator compound directly or indirectlywith a defined amount of propylene oxide to form an internal block ofoxypropylene groups, followed by further direct or indirect addition ofone or more other oxides.

The polyoxyalkylene polyether polyol may contain only ethylene oxidegroups, especially if the molecular weight is below 600. However, itpreferably contains from 50 to 100 weight % of oxypropylene groups,preferably from 70 to 96 weight % of oxypropylene groups, based on theweight of all of the cyclic ether groups added.

In one preferred embodiment of the invention, propylene oxide is addedto and reacted directly with the initiator compounds through thereactive hydrogen atom sites to form an internal block ofpolyoxypropylene groups. The structure of such an intermediate compoundcan be represented according to the following formula:

    R[(C.sub.3 H.sub.6 O).sub.w ]-.sub.2

wherein R is the nucleus of the initiator; w is an integer representingthe number of oxypropylene groups in the block such that the weight ofthe oxypropylene groups is from 50 to less than 100 weight percent, (or100 weight % if one desires to make a polyol based solely onoxypropylene groups and the initiator), based on the weight of allalkylene oxides added; and 2 represents the number of reactive sites onthe initiator molecule onto which are bonded the chains of oxypropylenegroups.

The polyether polyol may also comprise more than one internal block ofoxypropylene groups. By an internal block is meant that the block ofoxypropylene groups should be structurally located between the nucleusof the initiator compound and a different block of one or more differentkinds of oxyalkylene groups. It is within the scope of the invention tointerpose a block of different oxyalkylene groups between the initiatornucleus and the block of oxypropylene groups, especially if thedifferent oxyalkylene groups are also hydrophobic. In one preferredembodiment, however, the internal block of oxypropylene groups isdirectly attached to the nucleus of the initiator compound through itsreactive hydrogen sites.

The polyoxyalkylene polyether polyols used in the invention areterminated with isocyanate reactive hydrogens. The reactive hydrogensmay be in the form of primary or secondary hydroxyl groups, or primaryor secondary amine groups. In the manufacture of elastomers, it is oftendesirable to introduce isocyanate reactive groups which are morereactive than secondary hydroxyl groups. Primary hydroxyl groups can beintroduced onto the polyether polyol by reacting the growing polyetherpolymer with ethylene oxide. Therefore, in one preferred embodiment ofthe invention, the polyoxypropylene polyether polyol is terminated witha terminal block of oxyethylene groups. Alternatively, in anotherembodiment, the polyether polymer of the invention may be terminatedwith of a mixture of primary and secondary terminal hydroxyl groups whena mixture of ethylene oxide and, for example, propylene oxide isemployed in the manufacture of a terminal cap. Primary and secondaryamine groups can be introduced onto the polyether polymer by a reductiveamination process as described in U.S. Pat. No. 3,654,370, incorporatedherein by reference.

The weight of the terminal block of oxyethylene groups when employed, isat least 4 weight % to 30 weight %, preferably from 10 weight % to 25weight %, based upon the weight of all compounds added to the initiator.

The method of polymerizing the polyether polymers of the invention isnot limited and can occur by anionic, cationic, or coordinatemechanisms.

Methods of anionic polymerization are generally known in the art.Typically, an initiator molecule is reacted with an alkylene oxide inthe presence of a basic catalyst, such as an alkoxide or an alkali metalhydroxide. The reaction can be carried out under super atmosphericpressure and an aprotic solvent such as dimethylsulfoxide ortetrahydrofuran, or in bulk.

The type of catalyst used to manufacture the polyoxyalkylene polyetherpolyol is also not limited so long as the catalyst is of the type thatwill produce polyoxyalkylene polyether polyols having a degree ofunsaturation of 0.04 or less at the desired number average molecularweight. Suitable catalysts include the alkali metal compounds, alkaliearth compounds, ammonium, and double metal cyanide catalysts asdescribed in U.S. Pat. No. 3,829,505, incorporated herein by reference,as well as the hydroxides and alkoxides of lithium and rubidium. Otheruseful catalysts include the oxides, hydroxides, hydrated hydroxides,and the monohydroxide salts of barium or strontium.

Suitable alkali metal compounds include compounds that contain sodium,potassium, lithium, rubidium, and cesium. These compounds may be in theform of alkali metal, oxides, hydroxides, carbonates, salts of organicacids, alkoxides, bicarbonates, natural minerals, silicates, hydrates,etc. and mixtures thereof. Suitable alkali earth metal compounds andmixtures thereof include compounds which contain calcium, strontium,magnesium, beryllium, copper, zinc, titanium, zirconium, lead, arsenic,antimony, bismuth, molybdenum, tungsten, manganese, iron, nickel,cobalt, and barium. Suitable ammonium compounds include, but are notlimited to, compounds which contain ammonium radical, such as ammonia,amino compounds, e.g., urea, alkyl ureas, dicyanodiamide, melamine,guanidine, aminoguanidine; amines, e.g., aliphatic amines, aromaticamines; organic ammonium salts, e.g., ammonium carbonate, quaternaryammonium hydroxide, ammonium silicate, and mixtures thereof. Theammonium compounds may be mixed with the aforementioned basicsalt-forming compounds. Other typical anions may include the halide ionsof fluorine, chlorine, bromine, iodine, or nitrates, benzoates,acetates, sulfonates, and the like.

Of the alkali metals, cesium is the most preferred. Lithium, sodium, andpotassium are often not effective at reducing the degree of unsaturationof polyoxyalkylene polyether polyols at the higher equivalent weights.In a preferred embodiment, the polyoxyalkylene polyether polyols aremade with a cesium containing catalyst. Examples of cesium-containingcatalysts include cesium oxide, cesium acetate, cesium carbonate, cesiumalkoxides of the C₁ -C₈ lower alkanols, and cesium hydroxide. Thesecatalysts are effective at reducing the unsaturation of high equivalentweight polyols having a large amount of oxypropylene groups. Unlikedouble metal cyanide catalysts, which can also be effective at loweringthe degree of unsaturation of polyoxyalkylene polyether polyols, thecesium-based catalysts do not have to be removed from the reactionchamber prior to adding an ethylene oxide cap onto a polyether polyol.Thus, the manufacture of a polyoxypropylene polyether polyol having anethylene oxide cap can proceed throughout the whole reaction with acesium based catalyst.

The degree of unsaturation can be determined by reacting the polyetherpolymer with mercuric acetate and methanol in a methanolic solution torelease the acetoxymercuric methoxy compounds and acetic acids. Any leftover mercuric acetate is treated with sodium bromide to convert themercuric acetate to the bromide. Acetic acid in the solution can then betitrated with potassium hydroxide, and the degree of unsaturation can becalculated for a number of moles of acetic acid titrated. Morespecifically, 30 grams of the polyether polymer sample are weighed intoa sample flask, and 50 ml of reagent grade mercuric acetate is added toa sample flask and to a blank flask. The sample is stirred until thecontents are dissolved. The sample and blank flasks are left standingfor thirty (30) minutes with occasional swirling. Subsequently, 8 to 10grams of sodium bromide are added to each and stirred for two (2)minutes, after which one (1) ml of phenolphthalein indicates is added toeach and titrated with standard 1.0N methanolic KOH to a pink endpoint.The degree of unsaturation is calculated and expressed asmilliequivalents per gram: ##EQU1## The acidity correction is made onlyif the acid number of the sample is greater than 0.04, in which case itis divided by 56.1 to give milliequivalents/g.

The reaction conditions can be set to those typically employed in themanufacture of polyoxyalkylene polyether polyols. Generally, from 0.005percent to about 5 percent, preferably from 0.005 to 2.0 percent, andmost preferably from 0.005 to 0.5 percent by weight of the catalystrelative to the polyether polymer is utilized.

Any catalyst left in the polyether polymers produced according to theinvention can be neutralized by any of the well-known processesdescribed in the art, such as by an acid, adsorption, water washing, orion exchange. Examples of acids used in the neutralization techniqueinclude solid and liquid organic acids, such as 2-ethylhexanoic acid andacetic acid. For ion exchange, phosphoric acid or sulfuric acid may beused. Extraction or adsorption techniques employ activated clay orsynthetic magnesium silicates. It is desirable to remove metal cationiccontents down to less than 500 ppm, preferably less than 100 ppm, mostpreferably from 0.1 to 5 ppm.

As for other processing conditions, the temperature at whichpolymerization of the polyether polymers occurs generally ranges from80° C. to 160° C., preferably from 95° C. to 115° C. The reaction can becarried out in a columnar reactor, a tube reactor, or batchwise in anautoclave. In the batch process, the reaction is carried out in a closedvessel under pressure which can be regulated by a pad of inert gas andthe feed of alkylene oxides into the reaction chamber. Generally, theoperating pressures produced by the addition of alkylene oxide rangefrom 10 to 50 psig. Generating a pressure over 100 psig increases therisk of a runaway reaction. The alkylene oxides can be fed into thereaction vessel as either a gas or a liquid. The contents of thereaction vessel are vigorously agitated to maintain a good dispersion ofthe catalyst and uniform reaction rates throughout the mass. The courseof polymerization can be controlled by consecutively metering in eachalkylene oxide until a desired amount has been added. Where a block of arandom or a statistical distribution of alkylene oxides are desired inthe polyether polymer, the alkylene oxides may be metered into thereaction vessel as mixtures. Agitation of the contents in the reactor atthe reaction temperature is continued until the pressure falls to a lowvalue. The final reaction product may then be cooled, neutralized asdesired, and removed.

The polyol composition of the invention may include additional polyolsin addition to the PTMEG and the above-described polyether polyol. Forexample, polyols of other functionalities, i.e., greater than 2, may beincluded. Such polyols may be prepared as described above, except thatan initiator of higher functionality is used, such as glycerol,trimethylol propane, pentaerythritol, sorbitol, sucrose, and the like,and amines such as ethylenediamine, toluenediamine, and the like. Higherfunctional polyols may be incorporated either by physical blending ofthe finished polyols or by including a higher-functional initiator in amixture with the above-described difunctional initiator prior toreaction with alkylene oxide(s). Thus, a mixture of initiator compoundsmay be used to adjust the functionality of the initiator to a numberbetween whole numbers. If one desires to manufacture an elastomer havingonly a slight degree of crosslinking, a high proportion of an initiatorhaving a functionality of 2, to which is added relatively small amountsof tri- or higher functional initiator compounds, may be mixed togetherto arrive at an initiator having an average functionality close to 2 andup to 2.3. On the other hand, a larger proportion of tri- or higherfunctional initiator compounds can be mixed with a di-functionalinitiator compound when a higher degree of crosslinking is desired.

Other types of polyol may also be included in the polyol composition ofthe invention. For example, polyester polyols may be added to improvecertain mechanical properties of an elastomer such as tensile strengthand modulus of the urethane polymer. For some elastomeric applications,however, it is preferred to use only polyether polyols because they canbe more hydrolytically stable than polyester polyols, and they processwell due to their lower viscosities. Other polyols that can be employedin addition to the polyoxyalkylene polyether polymers of the inventionare hydroxyl terminated hydrocarbons, such as polybutadiene polyols,where a high degree of hydrophobicity is desired. Castor oils and othernatural oils may also be employed. In addition, polycaprolactones can beused to increase the tensile strengths of elastomers. Other polyetherpolyols may be added, and it is preferred that these polyether polyolshave a low degree of unsaturation to optimize the mechanical propertiesof the product.

Other ingredients in the polyol composition, besides the PTMEG and thepolyoxyalkylene polyether polyol, may include other polyols, chainextenders or curing agents, catalysts, fillers, pigments, UVstabilizers, and the like.

The above-described components of the polyol composition can be blendedtogether with standard mixing techniques, preferably in aPTMEG:polyether polyol weight ratio of from 20:80 to 95:5, althoughratios of greater than 95:5 may also be useful. If either of thecomponents (A) or (B) are solid, they should be liquified, preferably bymelting, prior to mixing. Preferably, the polyol composition of theinvention should form a homogeneous blend without visual phaseseparation. It may be necessary to adjust the relative molecular weightsof either or both of the components (A) and (B) in order to achieve ahomogeneous blend.

Depending upon the application of the elastomer, the average actualfunctionality of the blend should be from 1.5 to 3.0, preferably from1.95 to 2.3, and as low as 1.95 to 2.1. In these embodiments, polyolshaving functionalities outside of these ranges can be used so long asthe average functionality falls within the range. In one embodiment thatis preferred for certain applications, the functionality of the blendshould be maintained at 3.0 or less to avoid losing too much elongation,a desirable feature for certain elastomeric applications. Inapplications where high hardness, high tensile strength, and lowelongations are desired, it may be desirable for the actual averagefunctionality of the blend to exceed 3.0. For most elastomerapplications, the mean number average molecular weight for the polyolcomposition of the invention can range from 500 to 4000, preferably from900 to 3000.

One-component elastomers can be cured by moisture from the air.Two-component elastomers can be cured along with chain extenders withcompounds containing isocyanate reactive hydrogen. These chain extendersmay be contained in the polyol composition. Elastomers may be preparedusing the one-shot technique or the prepolymer technique. If theprepolymer technique is used, the polyol composition will usually befree of a chain extender during the manufacture of the prepolymer. Theprepolymer is then reacted with any remaining polyol composition whichat that point contains a chain extender. In the one-shot process, thepolyisocyanate is reacted at the outset with a polyol compositioncontaining the chain extender.

Chain extenders may be, and are typically, employed in the preparationof polyurethane elastomers. The term "chain extender" is used to mean arelatively low equivalent weight compound, usually less than about 250equivalent weight, preferably less than 100 equivalent weight, having aplurality of isocyanate-reactive hydrogen atoms. Chain-extending agentscan include water, hydrazine, primary and secondary aliphatic oraromatic diamines, amino alcohols, amino acids, hydroxy acids, glycols,or mixtures thereof. A preferred group of alcohol chain-extending agentsincludes water, ethylene glycol, 1,3-propanediol, 1,4-butanediol,1,10-decanediol, o,-m,-p-dihydroxycyclohexane, diethylene glycol,1,6-hexanediol, glycerine, trimethylol propane, 1,2,4-,1,3,5-trihydroxycyclohexane, and bis(2-hydroxyethyl) hydroquinone. Apreferred group of amine chain extenders includes1,3-diaminocyclohexane, piperazine, ethylenediamine, propylenediamine,and mixtures thereof.

Examples of secondary aromatic diamines include N,N'-dialkyl-substitutedaromatic diamines, which may be unsubstituted or substituted on thearomatic radical by alkyl radicals, having 1 to 20, preferably 1 to 4,carbon atoms in the N-alkyl radical, e.g., N,N'-diethyl-,N,N'-di-sec-pentyl-, N,N'-di-sec-hexyl-, N,N'-di-sec-decyl-, andN,N'-dicyclohexyl-p- and m-phenylenediamine, N,N'-dimethyl-,N,N'-diethyl-, N,N'-diisopropyl-, N,N,'-disec-butyl- andN,N'-dicyclohexyl-4,4'-diaminodiphenylmethane andN,N'-di-sec-butylbenzidine.

The amount of chain extender used may vary depending on the desiredphysical properties of the elastomer. A higher proportion of chainextender and isocyanate provides the elastomer with a larger number ofhard segments, resulting in an elastomer having greater stiffness andheat distortion temperature. Lower amounts of chain extender andisocyanate result in a more flexible elastomer. Generally, about 2 to70,, preferably about 10 to 40, parts of the chain extender may be usedper 100 parts of polyether polymer and PTMEG and any other highermolecular weight isocyanate reactive components.

Catalysts may be employed to accelerate the reaction of the compoundscontaining hydroxyl groups with polyisocyanates. Examples of suitablecompounds are cure catalysts which also function to shorten tack time,promote green strength, and prevent shrinkage. Suitable cure catalystsinclude organometallic catalysts, preferably organotin catalysts,although it is possible to employ metals such as lead, titanium, copper,mercury, cobalt, nickel, iron, vanadium, antimony, and manganese.Suitable organometallic catalysts, exemplified here by tin as the metal,are represented by the formula: R_(n) Sn[X--R¹ --Y]₂, wherein R is a C₁-C₈ alkyl or aryl group, R¹ is a C₀ -C₁₈ methylene group optionallysubstituted or branched with a C₁ -C₄ alkyl group, Y is hydrogen or anhydroxyl group, preferably hydrogen, X is methylene, an --S--, an --SR²COO--, --SOOC--, an --O₃ S--, or an --OOC-- group wherein R² is a C₁ -C₄alkyl, n is 0 or 2, provided that R¹ is C₀ only when X is a methylenegroup. Specific examples are tin (II) acetate, tin (II) octanoate, tin(II) ethylhexanoate and tin (II) laurate; and dialkyl (1-8 C) tin (IV)salts of organic carboxylic acids having 1-32 carbon atoms, preferably1-20 carbon atoms, e.g., diethyltin diacetate, dibutyltin diacetate,dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate,dihexyltin diacetate, and dioctyltin diacetate. Other suitable organotincatalysts are organotin alkoxides and mono or polyalkyl (C₁ -C₈) tin(IV) salts of inorganic compounds such as butyltin trichloride,dimethyl- and diethyl- and dibutyl- and dioctyl- and diphenyl- tinoxide, dibutyltin dibutoxide, di(2-ethylhexyl) tin oxide, and dibutyltindichloride. Preferred, however, are tin catalysts with tin-sulfur bondswhich are resistant to hydrolysis, such as dialkyl (C₁ -C₂₀) tindimercaptides, including dimethyl-, dibutyl-, and dioctyl-tindimercaptides.

Tertiary amines also promote urethane linkage formation, and includetriethylamine, 3-methoxypropyldimethylamine, triethylenediamine,,tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl- andN-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine,N,N,N',N'-tetramethylbutanediamine orN,N,N',N'-tetramethylhexanediamine, N,N,N'-trimethyl isopropylpropylenediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethylether, bis(dimethylaminopropyl)urea, dimethylpiperazine,1-methyl-4-dimethylaminoethylpiperazine, 1,2-dimethylimidazole,1-azabicylo[3.3.0]octane and preferably 1,4-diazabicylo[2.2.2]octane,and alkanolamine compounds, such as triethanolamine,triisopropanolamine, N-methyl- and N-ethyldiethanolamine anddimethylethanolamine.

To prevent the entrainment of air bubbles in the sealants or elastomers,a batch mixture may be subjected to degassing at a reduced pressure oncethe ingredients are mixed together. In the degassing method, the mixedpolyurethane formed ingredients can be heated under vacuum to anelevated temperature to react out or volatilize residual water. Byheating to an elevated temperature, residual water reacts with theisocyanate to liberate carbon dioxide, which is drawn from the mixtureby the reduced pressure.

Alternatively, or in addition to the degassing procedure, thepolyurethane forming ingredients may be diluted with solvents to reducethe viscosity of the polyurethane forming mixture. Such solvents shouldbe nonreactive and include tetrahydrofuran, acetone, dimethylformamide,dimethylacetamide, normal methylpyrrolidone, methyl ethyl ketone, etc.The reduction in viscosity of polyurethane forming ingredients aid theirextrudability. For sealant applications, however, the amount of solventshould be kept as low as possible to avoid deteriorating their adhesionto substrates. Other solvents include xylene, ethyl acetate, toluene,and cellosolve acetate.

Plasticizers may also be included in the A- or B-side components tosoften the elastomer and decrease its brittleness temperature. Examplesof plasticizers include the dialkyl phthalates, dibutyl benzylphthalate, tricresyl phosphate, dialkyl adipates, and trioctylphosphate.

In addition to solvents or plasticizers, other ingredients such asadhesion promoters, fillers, and pigments, such as clay, silica, fumesilica, carbon black, talc, phthalocyanine blue or green, titaniumoxide, magnesium carbonate, calcium carbonate, UV-absorbers,antioxidants, and HALS may be added in amounts ranging from 0 to 75weight percent, based upon the weight of the polyurethane. Other fillersinclude dissolved gels, plasticells, graded and coated calciumcarbonate, urea solids, the reaction product of hydrogenated castor oilswith amines, and fibers.

The polyurethane elastomers of the invention can be prepared by theprepolymer technique or in a one-shot process. The elastomers of theinvention can be prepared by a reaction injection molding technique, orin a cast process wherein the polyurethane forming ingredients are mixedtogether and poured into a heated mold into pressure. Other techniquesinclude conventional hand-mixed techniques and low pressure or highpressure impingement machine mixing techniques followed by pouringpolyurethane forming ingredients into molds.

In a one-shot process, the PTMEG and the polyoxyalkylene polyetherpolyol of the invention, catalysts, and other isocyanate reactivecomponents forming the polyol composition (also known as "B-side"components) are simultaneously reacted with an organic isocyanate("A-side" components). Once the B-side components are mixed together,the urethane reaction commences; and the ingredients are poured orinjected into molds to make cast elastomers, or may be extruded or spunto make thermoplastic polyurethane or spandex fiber.

In a prepolymer technique, all or a portion of the PTMEG and thepolyoxyalkylene polyether polyol having an end group degree ofunsaturation of 0.04 or less, and any other isocyanate reactive polyolsin the polyol composition, and usually without any chain extender, arereacted with a stoichiometric excess of the organic isocyanate to forman isocyanate-terminated prepolymer. Such prepolymers usually have freeNCO contents of 0.5 to 30 weight %, and for many elastomericapplications, have free NCO contents of from 1 to 15 weight %. Theisocyanate-terminated prepolymer is then reacted as an A-side componentwith any remaining B-side components to form a polyurethane elastomer.In some cases, all of the B-side components are in the form of an activehydrogen-terminated prepolymer. In other cases, only a portion of thepolyol composition is reacted with the stoichiometric excess of organicisocyanate to form an isocyanate terminated prepolymer, which issubsequently reacted with the remainder of the polyol composition, as atwo-component elastomer. An isocyanate-terminated prepolymer is usuallyreacted with the isocyanate reactive functionalities in the polyolcomposition at an NCO to OH equivalent ratio of at least 1.5:1.

Alternatively, an active hydrogen-terminated prepolymer can be preparedif all or a portion of the PTMEG and the polyoxyalkylene polyetherpolyol having an end group degree of unsaturation of 0.04 or less, andany other isocyanate reactive polyols in the polyol composition, andusually without any chain extender, are reacted with a stoichiometricdeficiency of the organic isocyanate to form an activehydrogen-terminated prepolymer. The prepolymer is then reacted as aB-side component with A-side components to form a polyurethaneelastomer.

In one embodiment of the invention, there is manufacture of a spandexfiber using the blends of the invention. Spandex is, by definition, ahard-segment/soft-segment-containing, urethane-containing polymercomposed of at least 85% by weight of a segmented polyurethane (orurea). The term "segmented" refers to alternating soft and hard regionswithin the polymer structure.

Spandex is typically produced using one of four different processes:melt extrusion, reaction spinning, solution dry spinning, and solutionwet spinning. All processes involve differing practical applications ofbasically similar chemistry. In general, a block copolymer is preparedby reacting a diisocyanate with the polyol composition of the inventionin a molar ratio of about 1:2 and then chain extending the prepolymerwith a low molecular weight diol or diamine near stoichiometryequivalence. If the chain extension is carried out in a solvent, theresulting solution may be wet- or dry-spun into fiber. The prepolymermay be reaction-spun by extrusion into an aqueous or non-aqueous diaminebath to begin polymerization to form a fiber or the prepolymer may bechain extended with a diol in bulk and the resulting block copolymermelt-extruded in fiber form. Melt spinning is conducted in a mannersimilar to the melt extrusion of polyolefins. Reaction spinning istypically carried out after reacting the polyol composition with adiisocyanate to form a prepolymer. The prepolymer is then extruded intoa diamine bath where filament and polymer formation occursimultaneously, as described in more detail in U.S. Pat. No. 4,002,711.

In another embodiment of the invention, there is provided athermoplastic polyurethane (TPU) elastomer made with the blends of theinvention. TPU is made by reacting a polyol composition comprising PTMEGand a polyoxyalkylene polyether diol having a low degree of unsaturationwith and organic diisocyanate to form a linear polymer structure. Whileother polyols with higher functionalities than 2 can be combined withthe diol, these should be used in minor amounts if at all. It ispreferable that the functionality of the initiators used to make thepolyoxyalkylene polyether polyols is 2, and that no initiators havingfunctionalities of over or under 2 are used, in order to make thepolymer chain linear. The same type of chain extenders as describedabove can be used, with the preferable chain extenders being thedifunctional glycols.

The reaction may be carried out in a one shot process or by theprepolymer technique. In the one shot process, the raw ingredients arefed into the reaction zone of an extruder, heated at a temperatureeffective for polymerization to occur, extruded onto a conveyor belt,and pelletized. The prepolymer technique is similar except that theprepolymer and chain extender are the materials fed into the reactionzone of the extruder. The type of extruder employed is not limited. Forexample, either twin or single screw extruders can be used.

The following examples further describe the invention.

Materials

Polyol A is a propylene glycol adduct of propylene oxide and ethyleneoxide having a 20 weight percent terminal cap of polyoxyethylene groupsand an internal block of polyoxypropylene groups, having a molecularweight of about 3000, and a degree of unsaturation of 0.069,manufactured using KOH as a polymerization catalyst.

Polyol B is a propylene oxide-ethylene oxide adduct of propylene glycolhaving a terminal cap of 20 weight percent polyoxyethylene groups and amolecular weight of 3000, manufactured using cesium hydroxide as apolymerization catalyst, with a degree of unsaturation of 0.025.

Polyol C is a propylene oxide-ethylene oxide adduct of propylene glycolhaving a 20 weight percent terminal cap of polyoxyethylene groups and amolecular weight of 2500, manufactured using cesium hydroxide as apolymerization catalyst to a degree of unsaturation of 0.016.

Polyol D is a propylene oxide-ethylene oxide adduct of propylene glycolhaving a 20 weight percent terminal cap of polyoxyethylene groups and amolecular weight of 1250, manufactured using cesium hydroxide as apolymerization catalyst to a degree of unsaturation of 0.008milliequivalents KOH/g polyol.

PTMEG is a polytetramethylene ether glycol manufactured fromtetrahydrofuran to the designated molecular weight.

EXAMPLES 1-12

In these Examples, the compression sets of cast elastomers made usingblends of PTMEG and polyether polyols having a high degree ofunsaturation exceeding 0.04 were compared against blends of PTMEG andpolyether polyols having degrees of unsaturation of 0.04 or less.

Diphenylmethane diisocyanate was reacted with the blends of polyetherpolyols in the kinds and amounts stated in Table 1 below, to a six (6)percent free NCO content. The prepolymers were then reacted with1,4-butanediol chain extender and cast into 1/4-inch plaques in a mold.Each plaque was allowed to heat cure and was then subjected to analysis.The modulus was tested according to ASTM D790, the tensile strength andelongation percent according to ASTM D412, the Graves tear according toASTM 624, using Die C, the resilience percent according to ASTM 2632-79,and a compression set according to ASTM D395 at 25 percent deformation.

The next two Tables (2 and 3) illustrate the retention of compressionsets across the board from 0 to 30 weight percent of the lowunsaturation polyether polyol blended with PTMEG. Table 2 illustratesthe physical properties of cast elastomers made by the same process,according to Example 1, also using a PTMEG/Polyol B blend. Table 3illustrates the same process, except using PTHF 2500/Polyol C blends.Table 4 illustrates the physical properties of cast elastomers made bythe same process, using PTHF 1000/Polyol D blends.

                                      TABLE 1                                     __________________________________________________________________________          PTMEG MOD                                                                              TEN-                                                                             ELONG.          COMP.                                         Example 2000 100% SILE % TEAR RESILIENCE SET SHORE                          __________________________________________________________________________    1     80/20 1050                                                                             2449                                                                             410  441 58     26  88                                         POLYOL B                                                                     Comparison 80/20 869 2443 599 440 55 49 76                                    A POLYOL A                                                                    2 70/30 990 2162 427 454 56 29 87                                              POLYOL B                                                                     Comparison 70/30 850 1894 505 366 52 73 78                                    B POLYOL A                                                                  __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        Compar-                                                                         ison C Example 3 Example 4 Example 5 Example 6                              ______________________________________                                        MODULUS 100/0    95/5     90/10  80/20  70/30                                   100% 1059 1034 985 904 857                                                    300% 1812 1613 1675 1360 1224                                                 TENSILE 2767 2465 2822 1848 1501                                              ELONG. % 468 556 513 494 450                                                  TEAR 502 509 458 460 375                                                      (GRAVES)                                                                      SHORE A 81 83 80 80 82                                                        RESI- 58 61 26 60 49                                                          LIENCE %                                                                      COMP. SET 21 14 9.1 20.2 28.2                                                 25%                                                                         ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Compar-                               Example                                   ison D Example 7 Example 8 Example 9 10                                     ______________________________________                                        MODULUS 100/0    95/5     90/10  80/20  70/30                                   100% 1059 1000 953 943 827                                                    300% 1812 1678 1601 1532 1367                                                 TENSILE 2767 2450 2461 2318 2035                                              ELONG. % 468 481 517 507 517                                                  TEAR 502 489 459 449 392                                                      (GRAVES)                                                                      SHORE A 81 80 79 81 79                                                        RESI- 58 60 60 58 61                                                          LIENCE %                                                                      COMP. SET 21 14.9 20.2 19.5 33                                                25%                                                                         ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________            Comparison                                                                          Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                       E 11 12 13 14 15                                                            __________________________________________________________________________    PROPERTY                                                                              100/0 90/10                                                                              80/20                                                                              70/30                                                                              60/40                                                                              50/50                                         MODULUS                                                                       100% 1281 1117 1098 984 888 726                                               200% 1872 1646 1562 1421 1249 978                                             TENSILE 2650 2734 *2748 2753 2324 2238                                        ELONGATION 278 333 *351 386 392 513                                           TEAR 414 359 347 345 325 337                                                  (GRAVES)                                                                      SHORE A 92 89 90 90 88 90                                                     RESILIENCE 52 52 49 46 41 44                                                  COMP. 22 24 25 24 38 47                                                       SET %                                                                       __________________________________________________________________________

The results in Table 1 show that blends of PTMEG made with conventionalpolyether polyols using standard potassium hydroxide catalysts withrelatively high levels of unsaturation drastically increased thecompression set up to 49, with severe increases in compression sets at70/30 weight ratios. In contrast, the compression set of PTMEG/polyetherpolyols with low degrees of unsaturation retained significantly lowcompression sets and kept the reduced compression sets even as theamount of low unsaturation polyether polyol was increased to 30 weightpercent. The compression set at 25% deflection does not deviate by morethan +/-15 when compared to an equivalent elastomer made at the samefree NCO content using only polytetramethylene ether glycol as thepolyol and the polyol composition. This was accomplished withoutsignificant reductions in other physical properties, such as Shore Ahardness, tensile strength, modulus, and tear strength.

The results in each of Tables 2-4 illustrates that cast elastomers madewith polyether polyols having low degrees of unsaturation can be usedand blended with PTMEG without sacrificing the compression sets of theelastomers. Elongation was generally improved with polyol compositionsaccording to the invention, and certain samples also demonstratedimproved resilience. Furthermore, other physical properties such asmodulus, tensile strength, and tear strength were not sacrificed and areadequately maintained throughout the wide range of blend ratios.

The invention has been described in detail with reference to preferredembodiments thereof. It should be understood, however, that variationsand modifications can be made within the spirit and scope of theinvention.

What is claimed is:
 1. A prepolymer comprising the reaction product of apolyisocyanate with a polyol composition wherein the polyol compositioncomprises:a polyoxytetramethylene ether glycol, and a difunctionalactive hydrogen compound-initiated polyoxyalkylene polyether polyolcontaining at least one hydrophobic block made from propylene oxide or amixture of propylene oxide and other cyclic ethers, said polyoxyalkylenepolyether polyol having a degree of unsaturation of not greater than0.04 milliequivalents per gram of said polyether polyol and a terminalgroup comprised of isocyanate reactive hydrogens, wherein the weightratio of said polyoxytetramethylene ether glycol to said polyoxyalkylenepolyether polyol ranges from about 99:1 to about 70:30 and wherein saidpolyol is capped with oxyalkylene groups derived from ethylene oxide inan amount of from 4 weight percent to 30 weight percent, based on theweight of all oxyalkylene groups.
 2. A prepolymer according to claim 1wherein said prepolymer is a hydroxyl terminated prepolymer obtained byreacting a stoiciometric excess of the polyol composition with thepolyisocyanate.
 3. A prepolymer according to claim 1, wherein saidprepolymer is an isocyanate terminated prepolymer having a free NCOcontent of 0.5 weight percent to 30 weight percent.
 4. An elastomercomprising the reaction product of a mixture comprising:(A) apolyisocyanate, (B) a polyol composition, and (C) optionally, an activehydrogen chain extender, wherein said polyol composition comprises:(1) apolyoxytetramethylene ether glycol, and (2) a difunctional activehydrogen compound-initiated polyoxyalkylene polyether polyol containingat least one hydrophobic block made from propylene oxide or a mixture ofpropylene oxide and other cyclic ethers, said polyoxyalkylene polyetherpolyol having a degree of unsaturation of not greater than 0.04milliequivalents per gram of said polyether polyol and a terminal groupcomprised of isocyanate reactive hydrogens, and wherein the weight ratioof said polyoxytetramethylene ether glycol to said polyoxyalkylenepolyether polyol ranges from about 99:1 to about 70:30 and wherein saidpolyol is capped with oxyalkylene groups derived from ethylene oxide inan amount of from 4 weight percent to 30 weight percent, based on theweight of all oxyalkylene groups.
 5. An elastomer as recited in claim 4,wherein the number average molecular weight of the polyol compositionranges from 1000 to
 4500. 6. An elastomer as recited in claim 4, whereinthe average functionality of the polyol composition ranges from 1.97 to2.1.
 7. An elastomer as recited in claim 4, wherein said polyetherpolyol has a degree of unsaturation of not greater than 0.03milliequivalents per gram of said polyether polyol.
 8. An elastomer asrecited in claim 4, wherein said polyether polyol has a degree ofunsaturation of not greater than 0.015 milliequivalents per gram of saidpolyether polyol.
 9. An elastomer comprising the reaction product of amixture comprising:(A) an isocyanate-terminated prepolymer having a freeNCO content of 0.5 weight percent to 30 weight percent, (B) an activehydrogen chain extender, and (C) optionally, a polyisocyanate differentfrom said prepolymer, said prepolymer comprising the reaction product ofa polyisocyanate with a polyol composition, wherein said polyolcomposition comprises:(1) a polyoxytetramethylene ether glycol, and (2)a difunctional active hydrogen compound-initiated polyoxyalkylenepolyether polyol containing at least one hydrophobic block made frompropylene oxide or a mixture of propylene oxide and other cyclic ethers,said polyoxyalkylene polyether polyol having a degree of unsaturation ofnot greater than 0.04 milliequivalents per gram of said polyether polyoland a terminal group comprised of isocyanate reactive hydrogens, andwherein the weight ratio of said polyoxytetramethylene ether glycol tosaid polyoxyalkylene polyether polyol ranges from about 99:1 to about70:30 and wherein said polyol is capped with oxyalkylene groups derivedfrom ethylene oxide in an amount of from 4 weight percent to 30 weightpercent, based on the weight of all oxyalkylene groups.
 10. An elastomeras recited in claim 9, wherein the number average molecular weight ofthe polyol composition ranges from 1000 to
 4500. 11. An elastomer asrecited in claim 9, wherein the average functionality of the polyolcomposition ranges from 1.97 to 2.1.
 12. An elastomer as recited inclaim 9, wherein said polyether polyol has a degree of unsaturation ofnot greater than 0.03 milliequivalents per gram of said polyetherpolyol.
 13. An elastomer as recited in claim 9, wherein said polyetherpolyol has a degree of unsaturation of not greater than 0.015milliequivalents per gram of said polyether polyol.
 14. An elastomercomprising the reaction product of a mixture comprising:(A) ahydroxyl-terminated prepolymer, (B) a polyisocyanate, and (C)optionally, an active hydrogen chain extender, said prepolymercomprising the reaction product of a polyol composition in astoichiometric excess with a polyisocyanate, wherein said polyolcomposition comprises:(1) a polyoxytetramethylene ether glycol, and (2)a difunctional active hydrogen compound-initiated polyoxyalkylenepolyether polyol containing at least one hydrophobic block made frompropylene oxide or a mixture of propylene oxide and other cyclic ethers,said polyoxyalkylene polyether polyol having a degree of unsaturation ofnot greater than 0.04 milliequivalents per gram of said polyether polyoland a terminal group comprised of isocyanate reactive hydrogens, andwherein the weight ratio of said polyoxytetramethylene ether glycol tosaid polyoxyalkylene polyether polyol ranges from about 99:1 to about70:30 and wherein said polyol is capped with oxyalkylene groups derivedfrom ethylene oxide in an amount of from 4 weight percent to 30 weightpercent, based on the weight of all oxyalkylene groups.
 15. An elastomeras recited in claim 14, wherein the number average molecular weight ofthe polyol composition ranges from 1000 to
 4500. 16. An elastomer asrecited in claim 14, wherein the average functionality of the polyolcomposition ranges from 1.97 to 2.1.
 17. An elastomer as recited inclaim 14, wherein said polyether polyol has a degree of unsaturation ofnot greater than 0.03 milliequivalents per gram of said polyetherpolyol.
 18. An elastomer as recited in claim 14, wherein said polyetherpolyol has a degree of unsaturation of not greater than 0.015milliequivalents per gram of said polyether polyol.
 19. A prepolymercomprising the reaction product of a polyisocyanate with a polyolcomposition wherein the polyol composition comprises:(A) apolytetramethylene ether glycol, and (B) a difunctional active hydrogencompound-initiated polyoxyalkylene polyether polyol containing at leastone hydrophobic block made from propylene oxide or a mixture ofpropylene oxide and other cyclic ethers, said polyoxyalkylene polyetherpolyol having a degree of unsaturation of not greater than 0.01milliequivalents per gram of said polyether polyol and a terminal groupcomprised of isocyanate reactive hydrogens, wherein the weight ratio ofsaid polytetramethylene ether glycol to said polyoxyalkylene polyetherpolyol ranges from about 99:1 to about 50:50 and wherein said polyol iscapped with oxyalkylene groups derived from ethylene oxide in an amountof from 4 weight percent to 30 weight percent, based on the weight ofall oxyalkylene groups.
 20. An elastomer comprising the reaction productof a mixture comprising:(A) a polyisocyanate, (B) a polyol composition,and (C) optionally, an active hydrogen chain extender, wherein saidpolyol composition comprises(1) a polytetramethylene ether glycol, and(2) a difunctional active hydrogen compound-initiated polyoxyalkylenepolyether polyol containing at least one hydrophobic block made frompropylene oxide or a mixture of propylene oxide and other cyclic ethers,said polyoxyalkylene polyether polyol having a degree of unsaturation ofnot greater than 0.01 milliequivalents per gram of said polyether polyoland a terminal group comprised of isocyanate reactive hydrogens, andwherein the weight ratio of said polytetramethylene ether glycol to saidpolyoxyalkylene polyether polyol ranges from about 99:1 to about 50:50and wherein said polyol is capped with oxyalkylene groups derived fromethylene oxide in an amount of from 4 weight percent to 30 weightpercent, based on the weight of all oxyalkylene groups.